1. Field of the Invention
The present invention relates to a communication system and a communication device including a remote controller performing remote control by transmitting remote control codes and a host device to be an operation target by the remote control codes, and particularly relates to a communication system and a communication device performing bidirectional communication between the remote controller and the host device by using a wireless network.
2. Description of the Related Art
Presently, remote control is widely applied in various information devices such as a television receiver and AV devices. In the present specification, a device body to be the operation target for the remote controller is generically referred to as a “host device”.
As a communication means for the remote controller, infrared communication has been used. The infrared communication has advantages such that it is inexpensive and that power consumption is low, however, the infrared communication has disadvantages such that it is limited to unidirectional communication and that there is directivity. On the other hand, when using a wireless network is used as the communication means, bidirectional communication can be performed between the remote controller and the host device and the communication range is expanded, however, there exists a problem that the power consumption is high. Hereinafter, a remote control system using the wireless network will be considered.
Many host devices such as the television receiver use a commercial AC power supply as a main power supply, which are capable of receiving wireless signals from the remote controller by allowing the devices to be constantly in a reception waiting state. On the other hand, the load for a battery will be excessive when applying the constant reception waiting state for the remote controller side which is driven by the battery. However, when the reception waiting state is intermittent in the remote controller for saving power consumption, it is not easy to perform information transmission to the remote controller triggered by the host device side.
Here, current consumption in a case of applying IEEE802.15.4 as the wireless network used when performing bidirectional communication between the remote controller and the host device will be explained as an example.
Electric current of approximately 30 mA (a general value in DC 3.0V) flows through a communication module of IEEE802.15.4 a general value in DC 3.0V in any of transmission, reception and the reception waiting state. When the remote controller is constantly in the reception waiting state, electric current of 30 mA constantly flows. When the capacity of an AA battery is 750 mAh, a battery lifetime in the constant reception waiting state of the remote controller is 750 mAh/30 mA=25 hours, namely, just one day.
On the other hand, when the remote controller is in a dormant state in which transmission/receiving operations are not performed, which realizes little power consumption. The remote controller with little battery consumption can be obtained by allowing the remote controller to be in the dormant state in all periods except periods when remote control codes are transmitted. When the remote controller transmits a remote control code, the code has several bytes. As a communication rate of IEEE802.15.4 is 250 kbps, a communication sequence including an acknowledgment (ACK) is completed for approximately one millisecond even when information necessary for communication such as a header is added. That is, electric current and time necessary for one transmission by the remote controller is 30 mA, 1 millisecond. When the capacity of an AA battery is 750 mAh, the number of times the remote controller can be operated is 750 mAh×60×60 seconds/0.001 seconds/30 mA=90,000,000 times. Assuming that the remote control is performed 1000 times in a day, it is possible to use the remote controller 90,000 days, which is a considerably long life. However, when the reception waiting state is intermittent in the remote controller, it is not easy to perform information transmission to the remote controller triggered by the host device side (as described above).
A user selects a menu item on a screen of the host device, for example, by using cursor buttons of the remote controller and presses a determination button to thereby fix the selection of the menu item. On the host device side, an application corresponding to the selected menu item is activated, then, the application generates transmission information to the remote controller. In this case, the user himself/herself operating the remote controller while watching the screen realizes that there is transmission of information triggered by the host device through the operation of the remote controller. However, it is difficult that the remote controller itself recognizes that there is processing executed on the host device side or transmission of information triggered by the host device side only through the operations such that the cursor buttons and the determination button are pressed.
Some methods may be cited for allowing the remote controller in the dormant state to receive transmission information triggered by the host device.
For example, an activation button is provided at the remote controller. When the host device desires to transmit information to the remote controller, a screen for promoting the user to press the activation button is displayed. When the user presses the activation button of the remote controller in accordance with the instruction of the screen, the remote controller is switched from the dormant state to the reception waiting state and can receive transmission information from the host device. After the communication ends, the remote controller becomes in the dormant state again.
However, in the method using the activation button, it is necessary that the screen display for promoting the user to press the activation button is performed on the host device side. The trouble of operating the activation button is given to the user, and it is forced to press the activation button regardless of intention of the user every time information is transmitted from the host device. The processing is stopped from the start of information transmission by the host device until the user presses the activation button.
When information transmission triggered by the host device side is performed, button operations of the remote controller are performed until reaching the information transmission in many cases. For example, the case in which the menu item on the screen of the host device is selected by using the cursor buttons of the remote controller and the determination button is further pressed to thereby fix the selection of the menu item corresponds to the case (as described above). When focusing attention to the point, a method can be considered, that is, the remote controller is allowed to be in the reception waiting state during a certain period of time from the last time when the user pressed the button of the remote controller, and the reception operation is subsequently performed when information is transmitted from the host device during the period, however, the state is changed to the dormant state when there is no information transmission to thereby suppress power consumption. For example, a communication system capable of extending reception waiting time until a reception means is operated after the remote controller has transmitted a remote control signal is proposed (for example, refer to JP-A-2001-111647 (Patent Document 1).
However, power consumption of the remote controller is not low when the remote controller is shifted to the reception waiting state every time the button is operated. When the reception time is 1000 milliseconds, the operation time is drastically increased as compared with the time of 1 millisecond during which electric current is consumed by transmitting the remote control code, therefore, the battery lifetime is reduced by the increase.
The time from the pressing of the button on the remote controller side (namely, from the transmission of the remote control code) until information transmission is started on the host device side is not always fixed, therefore, it is difficult to set suitable reception waiting time of the remote controller. For example, when processing such as an inquiry to the network interrupts processing of the application activated in accordance with the operation of the remote controller by the host device, the reception waiting time is not only irregular but also extremely increased. When the reception waiting time is set to the maximum value assumed to be necessary by considering the above, power consumption by the reception waiting operation generated every time button operation of the remote controller is performed will be increased.